Radio Habana Cuba: Dxers Unlimited Weekend edition for December 9, 2000
By Arnie Coro, radio amateur CO2KK
Hi! Welcome to the weekend edition of your favorite radio hobby show! I am Arnie Coro, radio amateur CO2KK, the host of this twice-weekly program devoted entirely to the promotion and development of this wonderful hobby ... our hobby, yours and mine: RADIO!!!
And here are the headlines: Despite much lower solar activity, band conditions on the higher frequencies are really very good; lots of hams around the world are enjoying the annual 10 meter contest now in progress. More about the contest and some very interesting propagation findings sorrounding contest activity later...
Item two: Non resonant wire loop antennas are a very worthwhile alternative in many locations that do no have enough space for a dipole and where a vertical may be troublesome by picking up too much noise. More about non resonant loops in Dxers Unlimited's antenna section...
Item three: More about why some AM broadcast band radios pick up Radio Havana Cuba at the very end of the dial, near 1700 kiloHertz... a FULL EXPLANATION of why this happens will give you an insight into how supeheterodyne receivers work...
As always, at the end of the show , Arnie Coro's exclusive, but not copyrighted, in the public domain HF plus 6 meters propagation forecast. Stay with me right here on this same short wave frequency and keep listening to Dxers Unlimited. Margarita Delgado is my sound engineer and producer. I am Arnie Coro, back with you in a few seconds....
You are tuned to Radio Havana Cuba, the name of the show is Dxers Unlimited and here is item one in detail: Although solar flux is now almost reaching the minimum for this rotation, the HF bands -- including 10 meters and even 6 meters -- continue to provide surprising openings. Here is a good example, one that you won't find in ANY, not a single HF PROPAGATION HANDBOOK. Here is how I found about it.... Friday evening I left my 10 meter band transceiver tuned to 28.500, my usual parking spot on 10, went to have dinner, came back and left the radio on... then, very late in the evening, when I finished answering Dxers Unlimited's fan's e-mail, I went to the radio to turn it off, only to hear a faint whisper coming out of the speaker... Listen, this was happening at one oçlock in the morning local time, 0600 UTC... I tuned the radio about a kiloHertz up in frequency, and PRESTO... an Argentinian station calling CQ Contest... Sure, LU5VV, Lima Uniform Five Victor Victor was calling CQ contest. For him it was still later in the evening his local time, but conditions on 10 were open, and he was working a lot of stations... SO, I switched to my South America Assymetric Sloping Dipole, and gave him a call, he came back to me immediately, and I had my first entry in the 10 meter band contest log!!! The time, 0604 UTC, four minutes past one oçlock in the morning local time, frequency 28.390 kiloHertz, mode SSB voice... a few minutes later I worked LU7YS on 28.470, also with a very nice signal.
NOW, it is really difficult to tell if this was Trans Equatorial Scatter or standard F2 layer propagation, which at that time should be better described as F layer, as during the hours of darkness there is not an F2 layer as such. Contacts like the one just described are what make amateur radio such an interesting hobby. If you just follow what the HF propagation manuals say, you would never work some very interesting DX stations... life is richer than theory, amigos!!!
By the way... I will continue participating in the contest after returning home from our studios Saturday afternoon!!!!
This is Dxers Unlimited's weekend edition... Loop antennas are really fascinating, both in theory and practice, and loops that are more than one-third of a wavelength in overall perimeter provide nice results when used as non-resonant antennas. Let me explain how this works... For example, I have installed, here at my ham radio station CO2KK, a wire loop that is about 28 meters overall length. It hangs at an inclination of about 30 degrees from the vertical, using my backyard avocado tree and a 14-meter high mast... The loop is fed using a length of open wire line, of about 400 ohms impedance, by the way this line is homebrew, and works really well, and it's about the cheapest efficient transmission line that existst!!!
Well, the open wire line ends in an air core balun that can be switched for a one to one or a four to one ratio. From there, a length of coaxial cable reaches my also homebrew PI network antenna tuner... As those of you familiar with antennas will realize the loop is too small for the 40 meter band, and just a bit short for 30 meters, and a bit long for 20 meters... It is more than a wavelength long on 15, 12 and 10 meters... Well, I must tell you that this non-resonant loop, is one of my best DX antennas from 10 megaHertz all the way to 29.7 megaHertz, and it also provides good signals, but not outstanding ones, on 40 meters.
Why do I talk here today about NON RESONANT loop antennas ? Well for one good solid reason... many of you Dxers Unlimited listeners live in areas where long antennas are hard or impossible to install, and these non-resonant loops are really COMPACT... see, my square 28 meter perimeter loop is only 7 meters per side, around 22 feet, which is the overall length required for a 15 meter band dipole... BUT, THE LOOP IS CAPABLE of providing not only high performance on 15, it also lets me work on 20 and 30 meters with a performance which in practice is much better than a dipole, plus providing 40 meter coverage too. The loop is made from no.14 bare copper wire, which by the way, according to the electrical codes and regulations of many countries is the minimum wire diameter required for external antennas.
Here are again the design parameters: it is a square loop, seven meters on each side, and in my case it was installed not vertically or horizontally, but at an angle of some 30 degrees which, by the way, generates some very interesting vertical take off angles too!!! This is an excellent receiving antenna for short wave listening too, and it is a very quiet skywire, because loops are closed antennas; they have no sharp ends that will pick up static electricity!!!
If you want to know about the KKL-SEVEN non=resonant wire loop antenna design by yours truly, Arnie Coro, just drop me an e-mail to arnie@radiohc.org, or send an Air Mail post card to Arnie Coro, Radio Havana Cuba, Havana, Cuba... Again, the KKL-SEVEN non-resonant loop antenna building instructions and graphic file are available just for the asking. Send e-mail or an Air Mail postcard with your request.
And before leaving the ever popular ANTENNA SECTION OF DXERS UNLIMITED, here is a brief comment from an amateur radio operator who is also a regular listener to the show: Arnie, just installed, as per your advice, three radials extending out from the lower end of my Sloper Antenna for the 30, 20 and 17 meter bands, just wanted to comment that the improvement in performance is simply outstanding... Well amigo, thanks for your nice comments, and I am sure that many amateurs who use sloping dipoles or sloping quarter wave antennas could benefit from your experience. A dding a set of from at least 3 to up to 8 and even 16 quarter wave radials at the low end of a sloper antenna, certainly does improve its performance. And as many of you know well, the SLOPER in any of its versions is one of the least costly and most efficient DX antennas. BY THE WAY... a sloper is NOT A GOOD ANTENNA for short range work on 80, 40 or 30 meters, because it has almost no Near Vertical Incidence Skywave radiation!!!!
You are listening to Radio Havana Cuba's radio hobby show... And here is item three in detail: Many RHC listeners are reporting that they can pick up our broadcasts at the very high-frequency end of the AM broadcast band, somewhere between 1650 and 1700 kiloHertz. Well, be assured that we are not broadcasting there at all... You are actually picking up our 6000 kiloHertz Eastern North America broadcast there, due to a very interesting and well known, to radio engineers, third harmonic mixing. Here is how it works: your AM broadcast band receiver local oscillator operates typically about 455 kiloHertz above the receiving frequency, so when you are tuning between 1690 and 1700 kiloHertz, the local oscillator of your radio is moving from 2145 to 2155 kiloHertz... NOW, if you multiply 2145 by 3, it equals to 6435 kiloHertz. Now follow me: multiply 2155 kiloHertz by three, you will get 6465 kiloHertz... So, when your AM broadcast radio is tuning between 1690 and 1700 your local oscillator is actually generating a third harmonic that is sweeping between 6435 kiloHertz and 6465 kiloHertz. Now follow the thread and subtract 455 kiloHertz, the radio's IF, or intermediate frequency, and you will immediately realize that you will be picking up the really powerful signals on the 49 meters or 6 megaHertz band from 5980 to 6010 kiloHertz -- and I mean really powerful short wave signals in that frequency range, because your AM broadcast band receiver's input circuits are not tuned to those frequencies, so it does take a lot of signal to make this very peculiar third harmonic mixing work. Nevertheless, it does work, and a lot of folks keep asking me. Arnie, is RHC broadcasting on the upper end of the AM band? And I keep explaining to them, NO WE ARE NOT, it is just the third harmonic of your receiver's local oscillator doing the trick!!!
If you want to go through the whole number crunching again, just visit Dxers Unlimited website and download today's Dxers Unlimited's script. YES INDEED, it is a very interesting reception, which is a classic example of the problems that superheterodyne receivers can generate!!!
And now amigos, as always at the end of the show, free of charge, in the public domain, quotable and printable, here is Arnie Coro's Dxers Unlimited's HF PLUS 6 meters propagation update and forecast: We are still now, as you hear the show, under the effect of a high speed solar wind that may generate high latitude geomagnetic disturbances. This is coming from a coronal hole in the SUN, but will soon subside. Solar activity will be LOW, and will start to move back up again by the middle of the week, reaching a peak of above 200 solar flux units around December 20th... So, we may perhaps enjoy another week or 10 days of worldwide 6 meter band openings, and the 10, 12 and 15 meter bands will go back into high gear with openings well past local sunset.
Don't forget to listen to the 10 meter band contest... tune from 28.4 to 28.9 megaHertz using the SSB mode and you will hear many amateurs exchanging their contest numbers. I will be working the contest too, probably around 21.9 megaHertz, yes, high up the band 28.9 to avoid the high power contestants -- after all, your's truly humble home brew rig for 10 meters is only a 50 watt output one. connected to a wire antenna!!!
See you there around 28.9 kiloHertz to say HELLO!!! And don't forget that your radio hobby related comments, signal reports, and ideas for this show are what keeps Dxers Unlimited on the air for YOU!!!
Arnie Coro CO2KK
Havana, Cuba
December 9, 2000Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
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